I
was thinking exactly the same way that O_G is above. (There are, quite rightly, lots of restrictions upon the use of any type of device which transmits radio waves, in order to avoid causing interference to other devices).
However a quick look at the Ofcom website shows that things have changed fairly recently. Quote:
"From spring 2018 it should be possible to buy mobile repeaters that improve signal strength inside the home provided that there is some signal outdoors. Note, however, that some websites currently offer mobile repeater products (signal boosters) that are illegal to use in the UK because they are poorly designed and can create interference to other mobile networks"
Source:
https://www.ofcom.org.uk/phones-telecoms-and-internet/advice-for-consumers/advice/improving-mobile-phone-reception
That led me to this company's website, which shows that such devices don't seem to come cheap:
https://www.mobilesignalboosters.co.uk/
It's worth noting though that the same Ofcom link also includes this:
"Operators . . . offer devices for the home . . . (EE’s Signal Box, O2’s Boostbox, Three’s Home Signal, Vodafone’s Sure Signal). These work by connecting to a router and sending traffic over the broadband network to increase [the] mobile signal".
i.e. there are devices available from (at least some) phone service providers which can be placed where there's a reasonably good mobile signal and then forward it to the user's home router, so that it makes the final hop across to the user's phone via their wi-fi system. (So it might be worth asking the relevant phone service provider if they can offer anything suitable).
However simply switching to a different network might be all that your daughter needs to do. I suggest that, before forking out for any expensive solution, she should ask visitors to her new home which phone provider they're with and what signal strength they're getting in her house. She might well find that there's another provider offering a decent strength signal at her address. (If your daughter does find that another provider can offer a decent signal, she should remember that she might be able to get a cheaper deal by going to a third-party service which uses that operator's masts. For example, if she finds that 02 has a decent signal where she is, she should look at GiifGaff, which uses the O2 network and is likely to be cheaper than 02 itself. Similarly, if she finds that EE provides a good signal, she might like to look as Asda Mobile's service, which is far cheaper but uses the same masts).